Activity-based probes (ABPs) for broad protein families will be used to establish protein-based activity profiles for the diagnosis/prognosis/staging of breast cancer and identification of new markers that can be used for more rapid clinical testing. Breast cancer is a highly heterogeneous disease containing at least eight distinct stages, the most prevalent type of non-skin cancer, and the second deadliest cancer among women in the United States. ActivX Biosciences will use two platforms, Xhibit and Xsite, to develop unique protein activity profiles of human breast tumor samples from different clinical stages, estrogen receptor status, and invasive states, and identify the components of these profiles that may be useful as markers for the disease. Phase I of this project will be a proof-of-principle study profiling four breast cancer mouse models using ABPs for serine hydrolase, cysteine protease, and nucleotide-binding proteins. This study will demonstrate that the ActivX technology can develop predictive profiles for breast cancers of different origins using biological samples that approximate those derived clinically. The diagnostics technology ultimately developed by this project will provide a more specific molecular origin of a particular cancer than current histology can provide, allowing for earlier breast cancer detection than is currently possible, and will provide a method for monitoring disease progression. The protein activity profiles and technology developed in this study will be commercialized either by ActivX or through partnerships or other commercial agreements with pharmaceutical, biotechnology, and diagnostics companies.